This invention relates generally to the field of turbochargers and, more particularly, to a turbocharger bearing system comprising a turbocharger shaft thrust collar positioned within a turbocharger center housing to provide a smaller overall turbocharger package, and an overall better stabilized turbocharger shaft operation.
Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the exhaust housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
The common shaft extending between the turbine and compressor is disposed through a turbocharger center housing that includes a bearing assembly for: (1) facilitating shaft rotating action; (2) controlling axially directed shaft thrust effects and radially directed shaft vibrations; (3) providing necessary lubrication to the rotating shaft to minimize friction effects and related wear; and (4) providing a seal between the lubricated assembly and the turbine and compressor housings. The common shaft as used in turbocharger applications is known to have shaft-rotating speeds on the order of 120,000 to 250,000 rpm or higher. Under such operating conditions it is imperative that the bearing assembly provide shaft axial and radial stabilization to maximize shaft balance, thereby maximizing turbocharger housing sealability and compressor/turbine wheel stability.
Various prior art turbocharger housing bearing assemblies include a first annular seal at a housing turbine-side axial end, a second journal bearing adjacent the first annular seal, a second journal bearing, a generally dead space between the first and second journal bearings, a thrust collar at a housing compressor-side axial end, and a second annular seal disposed adjacent the thrust collar. Configured in this manner, a conventional turbocharger housing is axially lengthy, the journal bearing are spaced relatively close together, and a relatively long moment arm or cantilever exists between the second journal bearing and the compressor wheel.
It is, therefore, desired that a turbocharger bearing system be constructed that provides a more compact turbocharger package and better shaft stabilization and balance when compared to conventional bearing assemblies. It is further desired that the bearing system be constructed to improve these properties without adversely impacting the lubricating and thrust load handling capabilities of the bearing system.
Turbocharger bearing systems, constructed according to principles of this invention incorporate (1) a pair of journal bearings disposed adjacent respective compressor and turbine ends of the center housing; (2) a pair of journal seals positioned at adjacent respective compressor and turbine ends of the center housing next to respective journal bearings; and (3) a thrust collar disposed within the center housing and interposed between the journal bearings, wherein the thrust collar is positioned at an approximate axial center of the housing and cooperates with a central housing flange to control axial shaft movement. Configured in this manner, bearing systems of this invention improve shaft stability and balance, reduce turbocharger package size, and improve center housing sealability.